Interstellar gas in nearby elliptical galaxies may be rare, but not unseen. Magnetic fields have not yet been detected there. On the theoretical side, a small scale dynamo may be the only way to maintain the magnetic field inside elliptical galaxies, resulting in a random magnetic field of strengths of a few µGauss and of a few hundred parsecs in scale (Moss and Shukurov, 1996).
5.1. Individual Galaxies and quasars (~ 200 kpc)
Most of the radio galaxies and radio quasars studied here are located beyond 20 Mpc. The polarization of distant radio elliptical galaxies (and of quasars) comes from synchrotron radiation from relativistic electrons moving in the magnetic fields located in the nucleus of these objects, and also in 2 polarized radio lobes (~ 200 kpc long), located on both sides of the optical elliptical galaxy or the optical quasar. The central optical nucleus of the galaxy or quasar exhibits linear polarization at submillimeter and millimeter wavelenghts, amounting to ~ 4% in several quasars (Flett & Murray, 1991). One-sided or two-sided jets connect the optical galaxy/quasar to the radio lobe(s). For a review, see Asseo & Sol (1987). A recent theoretical model of magnetic fields in decelerating relativistic radio jets is given in Laing (1996).
The Hubble diagram for the brightest optical galaxies in clusters, showing a good linear relation between the redshift z of the spectral lines and the apparent visual magnitude mv, also works for a subset of quasars. Basu (1994) showed that polarized quasars, i.e., quasars with a detectable value of optical linear polarization or of radio linear polarization, obey the Hubble relation between z and mv.
Some quasars seen through intervening halos of galaxies
(i.e., damped Ly
absorption systems) show higher value of RM (e.g.,
Oren & Wolfe 1995;
Kronberg 1994),
suggesting that the extra RM may come from these intervening galaxies.
Kronberg et al. (1996) studied the difference along a jet between the position angle of the image of a radio jet and the position angle of linear polarization, for a line of sight going close to two intervening galaxies. While the PA of the image can be bent by an intervening mass, the polarization PA cannot be bent, yielding the mass of the intervening galaxies.